The present invention relates generally to gas turbine engines, and, more specifically, to turbine rotor blades therein.
A typical gas turbine engine includes several rows or stages of turbine rotor blades which extract energy from hot combustion gases for rotating the corresponding turbine disks from which they extend. A high pressure turbine powers an upstream compressor, and a low pressure turbine typically powers an upstream fan in an aircraft turbofan engine application.
Air is pressurized in the compressor and mixed with fuel in a combustor for generating the hot combustion gases which flow through the turbine stages. A portion of the pressurized air is bled from the compressor for cooling the turbine blades for ensuring long life thereof.
More specifically, turbine blades have hollow airfoils with various cooling circuits therein for accommodating the different heat loads over the concave pressure and convex suction sides thereof which extend between opposite leading and trailing edges. The cooling air is delivered to the supporting dovetail of the blade and channeled radially outwardly through the dovetail and platform through the root of the airfoil and radially outwardly to its outer tip.
The leading edge of the airfoil first receives the hot combustion gases in the turbine flowpath, and typically requires a dedicated cooling circuit therefor. The trailing edge of the airfoil is relatively thin and typically includes a dedicated cooling circuit therefor. And, the midchord region of the airfoil typically includes multiple cooling legs or channels specifically configured for cooling this region of the airfoil.
The prior art is crowded with various cooling circuits and cooling features for cooling turbine rotor blades from root to tip and between the leading and trailing edges. The internal cooling circuits may be single radial flow channels typically along the leading and trailing edges, with multiple flow channels in between typically in the form of multi-pass serpentine flow channels.
Short turbulator ribs are typically found in the various internal flow channels of the airfoil for tripping the cooling air coolant to increase its heat transfer coefficient for improving cooling efficiency. The turbulators are typically in the form of straight ribs extending horizontally or along the chord axis of the airfoil, or they may be inclined relative thereto.
As the air flows radially outwardly and radially inwardly through the various flow channels inside the turbine airfoil heat is extracted from the metal sidewalls thereof for providing local cooling, with the cooling air then being discharged through various apertures throughout the airfoil. For example, the sidewalls of the airfoil typically include inclined film cooling holes which discharge the spent cooling air in corresponding films for providing a thermally insulating cooling air blanket over the external surface of the pressure and suction sidewalls as required.
The leading edge may have specialized showerhead holes, and the trailing edge may have various forms of trailing edge discharge holes. And, the tip of the airfoil typically includes additional outlet holes in the floor of the tip cavity thereof for additionally discharging the air from the internal cooling circuits.
Although stator nozzle vanes and turbine rotor blades may share in general various cooling circuits therein including film cooling holes and internal turbulators, the turbine blades operate under centrifugal force due to rotation thereof. Centrifugal force acts on the coolant being channeled through the circuits inside the airfoil and affects the cooling performance thereof.
The combination of the radial velocity of the coolant inside the flow channels of the airfoil and the rotary speed of the blade atop its supporting rotor disk creates a Coriolis force on the coolant which introduces secondary flow fields in the form of small vortices in addition to the main radial direction of the coolant. The Coriolis force affects heat transfer of the coolant as it is tripped by the internal turbulators of the airfoil.
In U.S. Pat. No. 5,797,726 and U.S. Pat. No. 6,331,098 preferred orientations of the turbulators are disclosed for enhancing cooling performance in conjunction with the Coriolis force. These patents include specifically slanted turbulators along the pressure and suction sides of the airfoil, and additional chevron turbulators having small clearances or gaps therein.
The relatively long slant turbulators cooperate with the Coriolis force on the coolant to enhance heat transfer along the length of the those turbulators. The chevron turbulators enjoy enhanced heat transfer when specifically used in conjunction with the Coriolis force, interrupted only by the axial gap within the chevron pair.
In both configurations, the short-height turbulators are integrally cast in the airfoil during the original manufacture thereof and are subject to typical manufacturing casting tolerances. The turbulators are relatively low and relatively narrow in the exemplary range of about 10–30 mils, and the gaps in the chevron turbulators may also be in this exemplary size range. Excessively sized gaps decreases the heat transfer effectiveness of the chevron turbulators, and narrow gaps are difficult to cast and also affect performance of the turbulators.
Accordingly, it is desired to provide a turbine rotor blade with improved turbulators for enhanced performance under the Coriolis force.